A concept of a cloud technology has been frequently discussed in recent years. An electronic device including an imaging device such as an imaging unit and an imaging element is expected to perform a function of a cloud terminal. It is also estimated that various types of electronic devices are connected with a cloud to realize a society providing connections between these electronic devices, between electronic devices and users, and between users and the cloud in the near future. In consideration of this social trend, there has been demanded development of imaging devices mounted on electronic devices which will be adopted in a network society using a cloud or the like.
Incidentally, for connecting various types of electronic devices with a cloud, various problems need to be solved, such as a large volume of communication and increase in power consumption. Technologies for increasing the volume of communication have been developed in communication fields. However, there may be a limitation to expansion of the volume of communication. Moreover, when wireless communication users increase in number with development of a network society, these users immediately struggle for an available volume of communication. In this case, communication bands may become insufficient. On the other hand, problems are arising from imaging devices in view of power consumption required for pixel signal processing, and power consumption during communication. Furthermore, when attention is paid to communication of images formed by imaging devices, problems of image sizes and volumes of communication for formed images (communication rates) also need appropriate solution.
There has been diligently promoted development of an imaging element driving method and a signal processing for lowering whole power consumption of imaging devices including imaging elements. More specifically, an electronic imaging device disclosed in Japanese Patent Application Lid-Open No. 2007-134805, for example, divides all pixels included in a solid-state imaging element into several divisional areas, and alternately reads pixels contained in each of the divisional areas to achieve low power consumption. On the other hand, a semiconductor device disclosed in Japanese Patent Application Laid-Open No. 2012-165168 includes an element array unit containing unit elements in matrix, and a signal processing unit containing signal processing circuits provided for each column to perform predetermined signal processing on the basis of unit signals output from the unit elements. In an element selection mode which requires only information on a part of the unit elements arranged in one row of the element array unit, the semiconductor device controls the function of the signal processing circuit corresponding to the unnecessary unit element such that this signal processing circuit comes into a lower power consumption state than a power consumption state in a normal operation mode.
Generally, an image formed by an imaging device is compressed before communication to reduce power consumption during communication. Several proposals have been presented as image compression signal processing. For example, there is known such a signal processing technology which reduces data to a volume smaller than all pixels (all imaging elements) on the basis of exposure control for imaging elements, and also eliminates a processing circuit required for data compression after analog-digital conversion (for example, see Non-Patent Document 1: Y. Oike and A. Ei. Gamal, A, “CMOS Image Sensor With Per-Column ΣΔ ADC and Programmable Compressed Sensing”, Solid-State Circuits, IEEE Journal of Volume 48, Issue 1). According to this technology, pixel signals received from imaging elements are randomly selected by a multiplexer, and input to analog-digital converters randomly selected to compress pixel signals received from the imaging elements in a final stage.